Polypeptide hormones can have very selective behavioral effects; however, the functional organization of the neuronal targets of these hormones and the cellular mechanisms by which they cause their effects are mostly unknown. To study these questions we are investigating effects and sites of action of the polypeptide egg-laying hormone (ELH) of Pleurobranchaea. Pleurobranchaea has been choosen for this study because its nervous system is accessible to neuronal circuit analysis and because ELH-containing extracts cause egg laying and a selective suppression of feeding behavior. Our working hypothesis is that feeding behavior is suppressed by a factor identical with or associated with ELH which acts directly on the circuitry controlling feeding. In proposed experiments, ELH will be radioactively labeled to high specific activity and purified. Sites of binding of the hormone will then be investigated by receptor binding assay and by autoradiography. In addition, experiments on the effect of purified ELH and other fractions of pedal ganglia, which have been shown to suppress "feeding" in the isolated nervous system, will be analyzed for their electrophysiological effects. We expect to identify targets of ELH by the above procedures and to determine whether they are widespread throughout the nervous system or are localized to a few strategically located cells.